1. Field of the Invention
The present invention relates to a method of synthesizing hollow silica. In more particular, the present invention relates to a method of synthesizing hollow silica from sodium silicate.
2. Description of the Related Art
In general, since a hollow sphere has an empty space therein, the hollow sphere not only represents low density, a great specific surface area, and high porosity, but also has a property allowing different materials to pass through the surface of the hollow sphere, so that the hollow sphere has been spotlighted.
Among them, a silica (SiO2) coated hollow sphere has been spotlighted for the use of solar cells, catalysts, sensors, Li-ion batteries, drug delivery systems, or adiabatic materials.
The silica-coated hollow sphere is fabricated by forming a monodispersed organic template, frequently using TEOS (Tetraethyl orthosilicate), silicic acid, or sodium silicate as a silica deriving source material, coating silica, which is formed from the silica deriving source material, on an outer portion (surface) of the monodispersed organic template, and then melting and removing the organic template so that only the silica covering the surface of the monodispersed organic template remains.
Hereinafter, a method of fabricating hollow silica according to the related art will be described.
First, in the case of the TEOS, the above monodispersed organic template is formed by using an oil-base medium, silica is coated on the outer portion of the monodispersed organic template, and the monodispersed organic template is removed, thereby fabricating the hollow silica.
In this case, the TEOS has a disadvantage in that the TEOS is used for only the organic template using the oil-base medium, but has an advantage in that the TEOS facilitates the synthesis of the hollow silica.
Therefore, when only the organic template formed by using the oil-base medium is used, the hollow silica is fabricated by using only the TEOS.
In the case, the monodispersed organic template formed by using the oil-base medium may be more easily fabricated in size of several micrometers or more.
Meanwhile, in order to prevent a monodispersed organic template from being separated from a sodium silicate when the sodium silicate is used to form the hollow silica, an organic template formed by using a water-base medium is used.
In this case, due to the reactive characteristic of the water-base medium, the monodispersed organic template having the size of nanometers may be more easily formed, but the monodispersed organic template may not be formed in the size of several micrometers or more.
In other words, when the sodium silicate is used as a source material to from the hollow silica, fabricating hollow silica particles having the size of micrometers is significantly difficult.
In this case, the size of the hollow silica particle is important because hollow silica particles having the size of several micrometers or more are advantageous when the hollow silica particles are used as reflective adiabatic materials.
When the hollow silica is used as the reflective adiabatic material, the size of the hollow silica exerts a significant influence on the reflectance thereof. When the hollow silica has the size of micrometers rather than the size of nanometers, the hollow silica represents superior reflectance. Accordingly, the hollow silica having the size of micrometers represents superior performance as an adiabatic material.
Therefore, when considering the performance of the adiabatic material, it is necessary to synthesize the hollow silica in the size of several tens nanometers, preferably, several (tens) micrometers or more instead of nanometers.
In this regard, to synthesize monodispersed hollow silica having the size of several micrometers, it is natural to require the monodispersed organic template having the size of several micrometers.
However, since it is difficult to fabricate the monodispersed organic template having the size of several micrometers when the water base material is used, it is difficult to synthesize the hollow silica having the size of several micrometers while using sodium silicate.
However, although the hollow silica having the size of several micrometers may be easily formed if the TEOS is used, the TEOS is a very high-price material. Accordingly, it is necessary to fabricate the monodispersed hollow silica through an economical scheme.
In this case, the sodium silicate among the silica deriving source materials is the cheapest material in terms of an economical aspect. Accordingly, when the hollow silica is synthesized, the scheme of using the sodium silicate is very preferable.
In this case, as described above, when the sodium silicate is used as the silica driving source material, the monodispersed organic template formed by using the water base material must be used. Accordingly, it is difficult to fabricate the monodispersed organic template having the desirable size of several micrometers to several tens micrometers.